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Supporting Information
Bio-supported palladium nanoparticles as phosphine-free catalyst for Suzuki reaction in water
Peipei Zhou, Huanhuan Wang, Jiazhi Yang, Jian Tang, Dongping Sun*, Weihua
Tang*
School of Chemical Engineering, Nanjing University of Science and Technology,
Nanjing 210094
[email protected]; [email protected]
Contents Experimental…..…………….………………...……………………………………..S2 Instrumentation……………...………….………………….…….…………………..S2 TEM images and analysis of Pd/BC nanocomposites…..…………….….……...…..S3 XRD analysis……………...………….………………….…….…...………………..S4 TGA analysis……………...………….………………….…….…...………………..S4 Fourier infrared spectroscopic analysis………………………………………..…….S5
XPS analysis……………...………….………………….…….…...………….……..S6 General protocol for Suzuki coupling with different arylboronic acids…………...…....S7 Recyclability and Pd-leaching study…………………………………….…...……....S7 Coupling in water……………...………….………………….…….…...…………...S8 Coupling in DMF with organic base…….………………….…….…...……...……...S9 Suzuki coupling reaction of iodobenzene series………….…….…...……...….…...S10 Suzuki coupling reaction of chlorobenzene series……….…….…...……...….…....S11 Mechanism of Suzuki reaction……………...…………………...………….…..…..S12
1H NMR of biphenyl…………...………………………………..………….…..…..S13
1H NMR of 4-methylbiphenyl…………...………………………..……..…..….…..S14 1H NMR of biphenyl-4-carbaldehyde…...…………………………….………..…..S15 1H NMR of biphenyl-4-carbonitrile……...…………………………..……………..S16 1H NMR of 2-methoxybiphenyl………...………………………….…………….....S17
1H NMR of 3-methoxybiphenyl.………...…………………………..….…………..S18
1H NMR of 4-methoxybiphenyl………………..……………………..………….....S19
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Experimental Unless stated otherwise, all operations were performed in air with no special
considerations. All chemicals and solvents were purchased from Sigma-Aldrich, and
used as received.
Pd/BC nanocomposites were synthesized in the lab by following the protocol as
below. The two-step preparation protocol involves a first biosynthesis of BC
nanofibers (J. Z. Yang, J. W. Yu, J. Fan, D. P. Sun, W. H. Tang, X. J. Yang, J. Hazard.
Mater., 2011, 189, 377) and a followed hydrothermal reaction. With the purified BC
nanofibers (water content 98.4%) at hand, a typical hydrothermal reaction proceeded
as follows: immersing PdCl2 or Pd(NO3)2 (containing 0.1 g Pd) and freshly-prepared
BC nanofibers (3 g) into 50 mL DI water; degassing for 0.5 h before heating up to
140oC with vigorous stirring (1200 rpm) under N2 atmosphere; adding potassium
borohydride (2 g in 50 mL water) over 5 h; centrifuging and washing with water to
obtain the titled composites.
Instrumentation 1H NMR spectra were recorded on Bruker AVANCE 500 MHz (Bio-Spin
Corporation, Europe) spectrometer at room temperature in CDCl3 unless otherwise
specified. Chemical shifts are reported with respect to internal solvent, 7.26 ppm (1H,
CDCl3). The morphology of pristine BC and Pd/BC hybrid nanofibers was
investigated by means of TEM (JEM-2100). The crystallinity and the phase
composition of samples were characterized by XRD (Bruker D8 ADVANCE). FT-IR
spectra were obtained using a Bomen MB154S Fourier transform infrared (FTIR)
spectroscopy. X-ray photoelectron spectroscopy (XPS) measurements were performed
on a PHI-5300 X-ray photoelectron spectrometer with an Mg Kα excitation source
(1253.6 eV). Thermogravimetric analyses (TGA) were performed on a Boyuan
DTU-2C thermogravimetric analyzer from 50 to 800°C at a heating rate of 10°C/min-1
in nitrogen flow.
Specific surface area of samples were obtained by BET method using BET
instrument (NOVA 1000, Quanta Chrome, America).
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Elemental analyses of Pd/BC catalyst before as well as after 5-cycle reactions
were performed on a Perkin Elmer Optima 3300 DV ICP-AES. 5 mg of each sample
was dissolved in 2.5 mL of concentrated aqua regia and the volume was adjusted to
50 mL in a volumetric flask. This solution was then used for the elemental analysis.
TEM images and analysis of Pd/BC nanocomposites
The TEM images of pristine BC nanofibers and the BC nanofiber-supported
palladium nanoparticles during different hydrothermal reaction time are presented in
Figure S1.
Figure S1.TEM images of pristine BC nanofibers (a); and catalyst after hydrothermal reaction for 1 h (b), 2 h (c), 3 h (d) during palladium growth.
The TEM image of Figure S1a shows the TEM image of BC nanofibers
biosynthesized by Acetobacter xylinum NUST5.2, with an average diameter of about
30 nm and a length ranging from micrometers up to dozens of micrometers. TEM
images of final product are shown in Figure 1d, where the deposited Pd nanocrystals
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were well-dispersed on BC nanofibers with ~12 nm diameter. TEM images of the
growth of Pd nanoparticles on BC nanofibers during hydrothemal reaction for 1 h, 2 h
and 3 h are shown in Figure 1b, 1c and 1d, respectively. As shown in Figure 1b, the
deposited Pd nanocrystals were well-dispersed on BC surface with about 20 nm
diameter. The Pd obtained after 2 h reduction reaction exhibited same particle size,
but the number of Pd nanocrystals witnessed a slight increase (Fig. 1c). For prolonged
reaction duration (3 h), the number of Pd nanoparticles achieved a significantly
increase and the diameter of Pd nanoparticles was still about 20 nm (Fig. 1d).
XRD analysis
The crystallographic behavior of the deposited Pd nanoparticles was further
investigated by X-ray diffraction (XRD). From the XRD spectra shown in Figure S2,
broad peaks are observed at 2θ values of 40.21°, 47.05°, and 67.81°, which are
characteristic peaks for Pd and can be assigned to the crystallographic plane of (111),
(200) and (220) reflection of Pd. All of the diffraction peaks match well with those of
the perfect fcc Pd crystal structure. No extra peaks are detected in this pattern,
indicating clean Pd/BC composites achieved without any impurities.
30 40 50 60 70
Pd(111)
Pd(200)
Pd(220)
Inte
nsity
2θ(degree)
Figure S2. X-ray diffraction (XRD) patterns of Pd/BC catalyst.
TGA analysis
Suzuki coupling usually requires heating conditions; hence, the thermal properties
of the catalyst have a great impact for its catalytic activity and recyclability. The
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thermal stability of the pristine BC fibers and Pd/BC hybrid nanofibers was evaluated
by thermogravimetric analysis (TGA) in nitrogen flow (Fig. S3). It is apparent that
Pd/BC hybrid nanofibers exhibited the similar thermal stabilities as BC nanofibers, as
weight loss less than 5% on heating to 300oC. Upon continuous heating up to 600oC,
pure BC degrades completely, leaving only minute amounts, while 40% of the sample
still remains in Pd/BC.
100 200 300 400 500 600 700 8000
20
40
60
80
100 Pd/BC BC
Weig
ht lo
ss(w
%)
Temperature(oC)
Figure S3. TGA traces of BC nanofibres and Pd/BC catalyst recorded at a heating rate of 10oC/min under nitrogen flow.
Fourier infrared spectroscopic analysis (FTIR)
As observed from the FTIR spectra of pristine BC fibers and Pd/BC
nanocomposites, we can find that no change occurred between two spectra. It
indicated that Pd was deposited on the surface of BC fibers without chemical bonding
and thus Pd did not change the original structure of BC fibers.
3500 3000 2500 2000 1500 1000 500-100
-50
0
50
100
150
200
250
BC Pd/BC
%Tr
ansm
ittan
ce
Wavenumber(cm-1)
Figure S4. FTIR of BC nanofibers and Pd/BC catalyst.
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XPS analysis
Further evidence of the high crystal quality was obtained with X-ray photoelectron
spectroscopy (XPS). Figure S5 (a) and (b) showed the loaded Pd nanoparticles did not
change the valence state of C and O of BC fibers, indicating that Pd was deposited on
the surface of the BC nanofibers without chemical bonding. The Pd 3d spectra,
characterized by spin–orbit splitting (Pd 3d5/2 and Pd 3d3/2 components), shows values
of 334.8 and 339.8 eV, respectively. Both peaks originating from Pd agree well with
the binding energies for Pd0 (3d5/2 334.9 eV, 3d3/2 340.4 eV) state (D. Klemm, B.
Heublein, H. P. Fink, A. Bohn, Angew. Chem. Int. Ed., 2005, 44, 3358).
275 280 285 290 295
0
2
4
6
8
10
12
14
16
Inte
nsity
(a.u
.)
Binding energy (eV)
BC Pd/BC
(a)
525 530 535
0
2
4
6
8
10
12
14
16
Inte
nsity
(a.u
.)
Binding energy (eV)
BC Pd/BC
(b)
342 340 338 336 334 332 330
4
5
6
7
8
9
10334.8
339.8
Inte
nsity
(a.u
.)
Binding energy (eV)
(c)
Figure S5. XPS analysis of the BC nanofibres and Pd/BCF catalyst: (a) the XPS analysis of C; (b) the XPS analysis of O; (c) the XPS analysis of Pd.
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General protocol for th e Suzuki coupling with different ar ylboronic ac ids. Aryl
halide (1.2 equiv), arylboronic acid (1.2 equiv), base (2 equiv) and solvent (15 mL)
were added to a 50 mL round bottom flask. The solution was stirred in a heated oil
bath at 85°C. Pd/BC (0.05 mol%) was added into the stirring solution and the system
capped with a glass septum and allowed to react for 3.5 h.or for the time indicated.
The reaction mixture was cooled to room temperature prior to filtration. The Pd/BC
nanocomposites were washed with ethyl acetate (3×30 mL) and then deionized water
for recycling. The collected filtrate was extracted with ethyl acetate and washed with
water. After drying the extract with anhydrous MgSO4, the organic solvent was
removed by evaporation. The crude product was recrystallized with petroleum ether. Recyclability and Pd-leaching study:
For practical applications of heterogeneous systems, the lifetime of the catalyst and its
level of reusability are very important factors. To clarify this issue, we established a
set of experiments for the coupling of idobenzene with varied arylboronic acid (all
entries in Table 2) using the recycled Pd/BC catalyst. After the completion of the first
reaction to afford the corresponding biphenyl, the catalyst was filtered out, washed
with ethyl acetate, and transferred to the reaction flask for the second-cycle reaction.
A new reaction was then performed with fresh reactants under the same conditions.
The Pd/BC catalyst could be used at least 5 times without any change in activity.
Pd leaching was studied by ICP-AES analysis of the catalyst before and after the
five reaction cycles. The Pd concentration was found to be 5.29% before reaction and
5.26% after the reaction, which confirmed negligible Pd leaching; this is probably due
to the protection from the order bound water molecules covering around BC fibers via
H-bonding (Scheme S1). Also, no Pd metal was detected in the final coupling
product.
Scheme S1 illustrates the entire procedure of the fabrication of Pd/BC. At the
beginning, when BC was added into the PdCl2 solution, the Pd2+ coordinate with two
adjacent C2 and C3-hydroxyl groups in the same glucose units along the BC
backbone. Subsequently, when potassium borohydride solution was added into the
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colloidal mixture, the Pd2+ was reduced to Pd. The as-prepared Pd nanoparticles were
stabilized on the BC surface via coordination effect between Pd and hydroxyl groups
of BC. This growth mechanism is in good agreement with the above-presented TEM
photographs.
Scheme S1. Schematic preparation of Pd/BC catalyst.
Coupling with palladium prepared from Pd(NO3)2: iodobenzene (1.2 g, 6 mmol,
1.2 eq), phenylboronic acid (0.61 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs phenylboronic acid), final product as a
pale yellow solid (0.749 g, 97%). The catalyst was recycled to repeat the reaction
twice. Yield of cycle 2 - 96%, yield of cycle 3 - 94%.
Coupling with palladium prepared from PdCl2: iodobenzene (1.2 g, 6 mmol, 1.2
eq), phenylboronic acid (0.61 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq), H2O
(15 mL), Pd/BC (0.5 g, 0.05 mol% vs phenylboronic acid), final product (0.755 g,
98%). The catalyst was recycled to repeat the reaction twice. Yield of cycle 2 - 97%,
yield of cycle 3 - 96%.
Coupling in water: iodobenzene (1.2 g, 6 mmol, 1.2 eq), phenylboronic acid (0.61
g, 5 mmol, 1 eq) and K2CO3 (1.38 g, 10 mmol, 2 eq) were added to a RB flask with
DI H2O (15ml), the flask was placed in an oil bath until the temperature reached 85oC
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and the solution stirred until the base was completely dissolved. Pd/BC (0.5 g, 0.05
mol% vs phenylboronic acid) was added to the stirring solution and the system
capped with a glass septum and allowed to react for 3.5 h. The reaction mixture was
cooled to room temperature prior to filtration. The Pd/BC nanocomposites were
washed with ethyl acetate and then deionized water for recycling. The collected
filtrate was extracted with ethyl acetate and washed with water. After drying the
extract with anhydrous MgSO4, the organic solvent was removed by evaporation. The
crude product was recrystallized with petroleum ether to give diphenyl as a pale
yellow solid (0.749 g, 97%). The catalyst was recycled to repeat the reaction twice.
Yield of cycle 2 - 96%, yield of cycle 3 - 94%.
Coupling in DMF w ith organic base: iodobenzene (1.2 g, 6 mmol, 1.2 eq),
phenylboronic acid (0.61 g, 5 mmol, 1 eq) and triethylamine (1.45 mL, 10 mmol, 2 eq)
were added to a RB flask with DMF (15 mL). The flask was placed in an oil bath until
the temperature reached 85oC and the solution stirred until the base was completely
dissolved. Pd/BC (0.5 g, 0.05 mol% vs phenylboronic acid) was added to the stirring
solution and the system capped with a glass septum and allowed to react for 3.5 h.
The Pd/BC nanocomposites were washed with ethyl acetate and then deionized water
for recycling. The collected filtrate was extracted with ethyl acetate and washed with
water. After drying the extract with anhydrous MgSO4, the organic solvent was
removed by evaporation. The crude product was recrystallized with petroleum ether to
offer diphenyl as a pale yellow solid (0.598 g, 78%). The catalyst was recycled to
repeat the reaction twice. Yield of cycle 2 - 76%, yield of cycle 3 - 73%.
Scheme S2. Pd/BC for cross-coupling reactions in different reaction media.
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2 3 4 5 60
20
40
60
80
100
Yiel
d (%
)Reaction time (h)
Figure S5. Yield varying with reaction time for aqueous coupling in Scheme S2.
Suzuki coupling reaction of iodobenzene series
Biphenyl: iodobenzene (1.2 g, 6 mmol, 1.2 eq), phenylboronic acid (0.61 g, 5
mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq), H2O (15 mL), Pd/BC (0.5 g, 0.05 mol%
vs phenylboronic acid), final product (0.755 g, 98%). The catalyst was recycled to
repeat the reaction four times. Yield of cycle 2 - 97%, yield of cycle 3 - 96%, yield of
cycle 4 - 92%, yield of cycle 5 - 88%.
4-Methylbiphenyl: iodobenzene (1.2 g, 6 mmol, 1.2 eq), p-tolylboronic acid
(0.68 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq), H2O (15 mL), Pd/BC (0.5 g,
0.05 mol% vs p-tolylboronic acid), final product (0.773 g, 92%). The catalyst was
recycled to repeat the reaction four times. Yield of cycle 2 - 91%, yield of cycle 3 -
89%, yield of cycle 4 - 87%, yield of cycle 5 - 86%.
Biphenyl-4-carbaldehyde: iodobenzene (1.2 g, 6 mmol, 1.2 eq), 4-formylphenyl-
boronic acid (0.75 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq), H2O (15mL),
Pd/BC (0.5g, 0.05mol% vs 4-formylphenylboronic acid), final product (0.891 g, 95%).
The catalyst was recycled to repeat the reaction four times. Yield of cycle 2 - 92%,
yield of cycle 3 - 90%, yield of cycle 4 - 89%, yield of cycle 5 - 88%.
Biphenyl-4-carbonitrile: iodobenzene (1.2 g, 6 mmol, 1.2 eq), 4-cyanophenyl-
boronic acid (0.74 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mol, 2 eq) H2O (15 mL),
Pd/BC (0.5 g, 0.05 mol% vs 4-cyanophenylboronic acid), final product (0.788 g,
88%). The catalyst was recycled to repeat the reaction four times. Yield of cycle 2
-85%, yield of cycle 3 - 79%, yield of cycle 4 - 69%, yield of cycle 5 - 57%.
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2-Methoxybiphenyl: iodobenzene (1.2 g, 6 mmol, 1.2 eq),
2-methoxyphenylboronic acid (0.76 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5g, 0.05 mol% vs 2-methoxyphenylboronic acid), final
product (0.911 g, 99%). The catalyst was recycled to repeat the reaction four times.
Yield of cycle 2 -97%, yield of cycle 3 - 95%, yield of cycle 4 - 94%, yield of cycle 5
- 88%.
3-Methoxybiphenyl: iodobenzene (1.2 g, 6 mmol, 1.2 eq),
3-methoxyphenylboronic acid (0.76 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs 3-methoxyphenylboronic acid), final
product (0.903 g, 98%). The catalyst was recycled to repeat the reaction four times.
Yield of cycle 2-98%, yield of cycle 3 - 93%, yield of cycle 4 - 89%, yield of cycle 5 -
87%.
4-Methoxybiphenyl: iodobenzene (1.2 g, 6 mmol, 1.2 eq),
4-methoxyphenylboronic acid (0.76 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), final product (0.901 g, 98%). The catalyst was recycled to repeat the
reaction four times. Yield of cycle 2 -95%, yield of cycle 3 - 93%, yield of cycle 4 -
90%, yield of cycle 5 - 86%.
Suzuki coupling reaction of chlorobenzene series
Biphenyl: chlorobenzene (0.68 g, 6 mmol, 1.2 eq), phenylboronic acid (0.61 g, 5
mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq), H2O (15 mL), Pd/BC (0.5 g, 0.05 mol%
vs phenylboronic acid), final product (0.685 g, 89%).
4-Methylbiphenyl: chlorobenzene (0.68 g, 6 mmol, 1.2 eq), p-tolylboronic acid
(0.68 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq), H2O (15 mL), Pd/BC (0.5 g,
0.05 mol% vs p-tolylboronic acid ), final product (0.756 g , 90%).
Biphenyl-4-carbaldehyde: chlorobenzene (0.68 g, 6 mmol, 1.2 eq),
4-formylphenylboronic acid (0.75 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs 4-formylphenylboronic acid), final product
(0.837 g, 92% ).
Biphenyl-4-carbonitrile: chlorobenzene (0.68 g, 6 mmol, 1.2 eq),
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4-cyanophenylboronic acid (0.74 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs 4-cyanophenylboronic acid), final product
(0.671 g, 75%).
2-Methoxybiphenyl: chlorobenzene (0.68 g, 6 mmol, 1.2 eq),
2-methoxyphenylboronic acid (0.76 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs 2-methoxyphenylboronic acid), final
product (0.864 g, 94%).
3-Methoxybiphenyl: chlorobenzene (0.68 g, 6 mmol, 1.2 eq),
3-methoxyphenylboronic acid (0.76 g, 5 mmol, 1 eq), K2CO3 (1.38 g, 10 mmol, 2eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs 3-methoxyphenylboronic acid), final
product (0.837 g, 91%).
4-Methoxybiphenyl: chlorobenzene (0.68 g, 6 mmol, 1.2 eq),
4-methoxyphenylboronic acid (0.76g, 5 mmol, 1eq), K2CO3 (1.38 g, 10 mmol, 2 eq),
H2O (15 mL), Pd/BC (0.5 g, 0.05 mol% vs 4-methoxyphenylboronic acid), final
product (0.828 g, 90%).
Mechanism of Suzuki reaction
The mechanism of the Suzuki reaction is best viewed from the perspective of the
palladium catalyst. The first step is the oxidative addition of palladium to the halide 2
to form the organopalladium species 3. Reaction with base gives intermediate 4,
which via transmetalation with the boron-ate complex 6 forms the organopalladium
species 8. Reductive elimination of the desired product 9 restores the original
palladium catalyst 1.
Scheme S3. Schematic illustration of the mechanism of the Suzuki reaction.
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1H NMR of biphenyl
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1H NMR of 4-methylbiphenyl
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1H NMR of biphenyl-4-carbaldehyde
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1H NMR of biphenyl-4-carbonitrile
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1H NMR of 2-methoxybiphenyl
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1H NMR of 3-methoxybiphenyl
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